Hitherto, a device disclosed in, for example, Patent Literature 1 has been known as an exhaust gas purification device that purifies an exhaust gas flowing through an exhaust passage of an engine. The exhaust gas purification device disclosed in Patent Literature 1 includes a first casing that stores a DOC (Diesel Oxidation Catalyst) and a DPF (Diesel Particulate Filter), a pipe that is equipped with an injection nozzle (an injection device) that injects urea water (reduction agent) into the exhaust gas, and a second casing that stores an SCR (Selective Catalytic Reduction), where the pipe is inserted into the first casing so as to extend in a direction substantially perpendicular to the axial direction of the first casing and is connected to the second casing. Then, NOx of the exhaust gas is purified by the reduction using ammonia produced by the injection of the urea water.